Stabilized acrylonitrile polymers



Patented Dec. 1 1953 STABILIZED ACRYLONITBILE POLYMERS Robert J. Slocombe, Dayton, and George L. Wesp, Englewood, Ohio, assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware No Drawing; Application October 26, 1950, Serial No. 192,344

12 Claims. (Cl. 26045.'7)

V This invention relates to methods of preparing polymers of acrylonitrile which are stabilized with respect to thermodiscoloration. More specifically the invention relates to methods of con- 'verting unstable polymers of acrylonitrile into color stable polymers.

' Although polyacrylonitrile and copolymers of 50 percent or more by weight of acrylonitrile and other monomers containing olefinic unsaturation copolymerized therewith, are generally regarded as being materials of good thermostability, they are subject to discoloration. This phenomenon generally results because of the need for extruding and molding the composition at elevated temperatures. Furthermore, the higher acrylonitrile polymers find extensive use in the fabrication of fibers, films and fabrics which frequently are subjected to ironing operations at elevated temperatures. Thus, serious discolorations are often developed in the fabrication and processing of acrylonitrile polymers.

The primary purpose of this invention is to provide color stable polymers of acrylonitrile. A further purpose of the invention is to facilitate molding and other processing procedures without the danger of the deterioration of. fibers and other forms usually encountered at elevated temperatures. A still further purpose ofv the invention is to provide substances which can be added to conventional polymers to induce resistance to heat and discoloration. It has been discovered that by adding strontium compounds to acrylonitrile polymers improved resistance to discoloration may readily be developed. The nature of the chemical reaction involved is not definitely understood, but it is believed that the color change is due to some impurities present in the polymer. It may be that the strontium ions react with the impurity to form a substance which is more heat stable than the impurity in its original form. Since not all strontium compounds produce the same degree of beneficialiefiect the phenomena apparently involve additional stabilization by the anion as well as the cation. The total stabilization may involve additive or synergistic effects. Irrespective of the mechanism, it has been found that a very wide variety of strontium compounds produces the desired effect.

The acrylonitrile polymers with which this invention may be practiced include polyacrylonitrile and copolymers of from 20 per cent or more acrylonitrile and up to 80 per cent of one or more of a wide variety of other unsaturated substances known to be copolymerizable with the acrylonitrile. Thus, the invention is practicable with the well-known fiber forming copolymers of acrylonitrile, which may be the copolymers of per cent or more per cent of acrylonitrile and up to 25 per cent of other monomers. Other copolymers of from 25 per cent to 75 per cent acrylonitrileand '75 to 25 per cent of the various other monomers, which copolymers have primary utility in the field of film and molding composition production, are also useful.

The said other monomers with which the acrylonitrile may be copolymerized to produce resinous substances capable of use in the practice of this invention include vinyl acetate and other vinyl esters of monocarboxylic acids having up to four carbon atoms in the carboxylic acid radical, dimethyl maleate and dimethyl fumarate and other alkyl esters of fumaric and maleic acids, wherein the alkyl radical has up to four carbon atoms, methyl methacrylate or acrylate and other alkyl acrylates and alkyl methacryl'ates wherein the alkyl radical has up to four. carbon atoms, vinyl chloride and other vinyl halides, styrene, alpha-methylstyrene and other vinyl and isopropenyl substituted aromatic hydrocarbons, methacrylonitrile, vinylidene chloride, vinylpyridine, the vinyl derivatives of other alkyl substituted pyridines, and the vinyl derivatives of other compounds containing a tertiary amino atom in a heterocyclic ring, vinylchloroacetate and other vinyl esters of haloacetic acids, methallyl, chloroacetate, allyl chlor'oacetate and chloroallyl-chloroacetat-e, and the corresponding esters of other haloacetic esters, vinylimidazole and other N-vinyl derivatives of heterocyclic nitrogen compounds, and one or more of these and other unsaturated compounds known to be copolymerizable with acrylonitrile.

The .strontium salts which are useful in the practice of this invention include salts of both organic and inorganic acids, for example strontium chloride, strontium nitrate, strontium acetylacetonate, strontium maleate, and strontiumsulfate A wide variety of other strontium compounds may similarly be used. In the practice of this invention the strontium salt may be used to the extent of 0,01 per cent to ten per cent by weight of the acrylonitrile polymer to be stabilized. Preferred practice or" this invention involves the use of 0.1 per cent to three per cent of the stabilizer.

The invention may be practiced by combining the acrylonitrile polymer and the strontium compound by a wide variety of mechanical procedures. Thus, the polymer may be treated in 'vent is less critical.

compound within the solid polymer.

3 granular solid form and mixed physically with the solid strontium compound or an aqueous or other liquid solution or dispersion of the strontium compound. The physical mixture may take place at room temperature or at higher temperatures, for example the temperature at which the polymer is semi-solid or fluid. A preferred practice involves the use of solvents or plasticizers for the acrylonitrile polymers in the presence of which the intimate dispersing of the stabilizing additive and the acrylonitrile polymer is more readily eifected. The nature of the solvent which is useful in dissolving or softening the acrylonitrile polymer will to a large extent depend upon the chemical composition of the acrybutyrolactone, ethylene carbonate, maleic acid,

alpha-cyanoacetamide, and tris (dimethylamido) phosphate may be used.

In the treatment of the more soluble types of acrylonitrile polymers, for example those of from per cent to '75 per cent acrylonitrile and from per cent to 80 per cent of other monomers copolymerizable therewith, the selection of a sol- This type of copolymer may be dissolved or otherwise physically effected by the various ketones, esters and aromatic hydrocarbon types of solvents. mer is placed in a suitable solution, or softened and swelled by the selected medium so as to enable a more ready dispersion of the strontium Obviously a solvent which is also capable of dissolving at least to some extent th strontium compound to be used will be exceptionally beneficial. However, the selection of the dispersing agent, the

stabilizing agent and the particular method of dispersing the compound in the solid polymer is a matter readily determined by one skilled in the art.

To evaluate the stabilizing action of various compounds, acrylonitrile polymers of different chemical and physical properties were used and the strontium'compounds dispersed therein by a variety of methods.

Example Polyacrylonitrile was stabilized by dissolving it in N,N-dimethylformamide and adding to separate solutions two per cent of each of the various strontium salts in the table below. Films were prepared therefrom and tested to determine the in the percentage of the transmission in excess 6 of the transmission through a sample of the .In general, the copolyidentical polymer not containing the stabilizing agent using a 410 millimicron filter in the photometer.

Strontium chloride +26.0 0.6 Strontium nitrate +17.8 +202 Strontium maleate +343 +240 Strontium acetylacetonate +209 7.0

What we claim is:

1. A stable polyacrylonitrile polymer comprising a polymer of 20 per cent to 100 per cent of acrylonitrile and from up to 80 per cent of another olefinic monomer copolymerizable therewith, said polymer containing intimately dispersed therein as the sole stabilizing agent from 0.01 to ten per cent of a compound of the group consisting of strontium chloride, strontium nitrate, strontium maleate, strontium acetylacetonate, and strontium sulfate.

2. A stable polyacrylonitrile polymer comprising a polymer of 20 per cent to 100 per cent of acrylonitrile and from up to per cent of another olefinic monomer copolymerizable therewith, said polymer containing intimately dispersed therein as the sole stabilizing agent from 0.1 per cent to three per cent of a compound of the group consisting of strontium chloride, strontium nitrate, strontium maleate, strontium acetylacetonate, and strontium sulfate.

3. The stable polymer of claim 1 wherein the strontium salt is strontium chloride.

4. The stable polymer of claim 1 wherein the strontium salt is strontium nitrate.

5. A stable acrylonitrile polymer comprising a polymer of 20% to of acrylonitrile and up strontium salt is strontium nitrate.

10. A stable acrylonitrile polymer comprising a .polymer of 20% to 100% of acrylonitrile and up to 80% of another olefinic monomer copolymerizable therewith, said polymer containing intimately dispersed therein from 0.01% to 3% by weight of strontium maleate.

11. The stable polymer of claim 2 wherein the strontium salt is strontium acetylacetonate.

12. The stable polymer of claim 2 wherein the strontium salt is strontium sulfate.

ROBERT J. SLOCOM'BE. GEORGE L. WESP.

References Cited in the file of this patent UNITED STATES PATENTS Name Date Chaban May 9, 1950 Number 

1. A STABLE POLYACRYLONITRILE POLYMER COMPRISING A POLYMER OF 20 PER CENT TO 100 PER CENT OF ACRYLONITRILE AND FROM UP TO 80 PER CENT OF ANOTHER OLEFINIC MONOMER COPOLYMERIZABLE THEREWITH, SAID POLYMER CONTAINING INTIMATELY DISPERSED THEREIN AS THE SOLE STABILIZING AGENT FROM 0.01 TO TEN PER CENT OF A COMPOUND OF THE GROUP CONSISTING OF STRONTIUM CHLORIDE, STRONTIUM NITRATE, STRONTIUM MALEATE, STRONTIUM ACETYLACETONATE, AND STRONTIUM SULFATE. 